Integrated circuits are known to provide a plurality of outputs which am coupled to a multitude of circuits. Some of these circuits have high input impedance, such that the integrated circuit needs to supply a relatively low amount of current, (100 .mu.A). Other circuits have a relatively low input impedance such that the integrated circuit has to supply a substantial amount of current, (10-100 mA).
In many applications, an integrated circuit is capable of providing the necessary current. In other applications, when the output of an integrated circuit is driving a relatively low impedance, an external output buffer is generally used to provide the necessary current. Such external output buffers have a relatively high impedance and provide a substantial amount of current to the particular device being sourced by the integrated circuit.
Integrated circuits that perform telecommunication functions are also well known in the art. Such integrated circuits perform functions such as audio processing, audio compression, etc. In utilizing such integrated circuits, the output requirements for the driving integrated circuit are usually below 100 mA peak. As the need for higher data rate transmissions along twisted telephone wire pairs arises, present integrated circuits are incapable of driving the relatively low impedance of the telephone twisted wire pairs. For example, at a 1 megahertz (MHz) rate, the impedance of a twisted telephone wire pair is roughly 100 ohms. Typical voltage range on these types of high frequency data transfers is a swing of +or -5 volts. Thus, the amount of current needed is 100 mA average. An additional requirement of high data rate transmissions is that the fidelity, or total harmonic distortion, must be extremely high. For example, the total harmonic distortion must be in excess of 70 decibels (dB). Current integrated circuits, while able to supply 100 mA, cannot meet the fidelity requirements. Other circuits, while capable of meeting the fidelity requirements, cannot source the current.
One typical prior art technique to overcome this is to eliminate the use of integrated circuits and utilize discrete components. It is well known that discrete line drivers can supply the necessary currents and fidelity requirements, however, for portable communication devices, discrete components increase the size of the device. A second typical prior art technique would be to use integrated circuits having high fidelity and low current, and couple the output to a discrete high fidelity line driver. While both of these solutions provide the desired results, they require additional board space, components, and cost. Therefore, a need exists for integrated circuits that provide high current high fidelity output signals over a wide bandwidth without the need for external circuits.